This invention relates generally to liquid crystal displays (LCD's) and more specifically to a means for reducing unwanted scattered light and increasing the contrast in such displays.
A liquid crystal display generally consists of a film of liquid crystals (a substance which exists at a state between liquid and crystal) between two systems of electrodes. One electrode is transparent while the other reflects light. The reflective electrode consists of a plurality of integrated circuits mounted on a substrate material. Electrodes are electrically connected to each integrated circuit whereby selected portions of the reflecting electrode may be energized while other portions remain neutral.
When the integrated circuit becomes energized, the liquid crystal between the electrodes exhibits hydrodynamic turbulance and disperses light. The contrast between the dispersed light and the reflected light creates the figures of the display. The integrated circuit can also be used to energize a field effect liquid crystal material mode.
A foremost feature of the liquid crystal display is its ability to maintain high contrast under high ambient lighting conditions. The main factor limiting contrast in the LCD is light which is ramdomly scattered off steps in the semi-conductor wafer surface. Various methods and means have been advanced in an attempt to control light scattering, but thus far none of those provided have been able to eliminate the background scattering in the off state. A solution has been suggested which lowers light scattering by application of a smoothing layer within the crystal, thereby reducing the number of surfaces from which undesired light is reflected.
The smoothing layer, while improving the performance of the LCD continues to show indentations and other irregularities at the contact `via` holes. These holes are areas where substrate is selectively etched to provide the required electrical contacts. Unless a method and means is provided for "filling" these indentations, the contrast ratio and the field-of-view will be limited.